Delayed petroleum coking vessel inspection device and method

ABSTRACT

This invention comprises a system and a method for inspecting the inside of delayed petroleum coking vessels to identify deformations, detect and determine the severity of other defects, and visually observe the inside of the inspected vessel.

CROSS-REFERENCE TO RELATED CASES

This application is a continuation of application Ser. No. 15/383,951filed Dec. 19, 2016, now U.S. Pat. No. 9,940,702 issued Apr. 10, 2018,which is a continuation of application Ser. No. 14/826,109 filed Aug.13, 2015, now U.S. Pat. No. 9,524,542 issued Dec. 20, 2016, which is acontinuation-in-part of application Ser. No. 13/889,173 filed May 7,2013, which is a continuation of U.S. Pat. No. 8,436,898, formerlyapplication Ser. No. 13/104,453 filed May 10, 2011, and issued on May 7,2013, which is a continuation of U.S. Pat. No. 7,940,298, formerlyapplication Ser. No. 11/391,532 filed Mar. 28, 2006, and issued on May10, 2011, which claims the benefit of U.S. Provisional Application No.60/671,961, filed Apr. 15, 2005, and U.S. Provisional Application No.60/718,583, filed Sep. 19, 2005, all of which applications are herebyincorporated herein by reference, in their entirety.

FIELD OF THE INVENTION

The present invention relates to systems for use to inspect the insideof delayed petroleum coking vessels to detect cracks and other defects.

BACKGROUND OF THE INVENTION

In many industrial systems, large vessels are used for various purposes.In many instances, these vessels contain materials which are at hightemperature, high pressure or both and are vulnerable to failure. As aresult, it is necessary that the inside of such vessels be inspectedperiodically. In the past, such inspections have been accomplished bysimply emptying the vessel and physically inspecting the interiorsurfaces of the vessel. This permitted the detection of bulges, cracks,and pits and allowed for visual observation of the inside of the vessel.Some such vessels may be as large as twenty to thirty feet or more indiameter and fifty to seventy feet or more in height. One example ofsuch vessels is petroleum coking vessels. These vessels are exposed toboth thermal and mechanical stresses and are typically periodicallyinspected. The invention will be discussed primarily by reference todelayed petroleum coking vessels although the invention is equallyuseful with other large vessels.

Such vessels can be inspected by emptying the vessel and erectingscaffolding in the interior of the drum so that inspection personnel canmake essentially manual inspections, including dimensional measurementsto detect changes in the shape of the drum structure, visible defectsand the like. Not only is this expensive and time consuming, inspectionpersonnel are exposed to risks of released gases, falls and the likeduring the inspection process. Subsequently methods were developed, forinstance as disclosed in U.S. Pat. No. 5,425,279 issued to R. D. Clark,et al. on Jun. 20, 1995 (the '279 Patent), which is hereby incorporatedin its entirety by reference, for inspecting the interior of vesselsusing laser devices with reflective laser light being measured to detectand define bulges and other dimensional changes inside the vessel. Thislaser inspection technique was combined with the use of a video camerawith both the laser system and the video camera being operable toprovide recorded data by reference to the specific portions of thevessel tested. This data permitted the detection of bulges and the likeand visual examination of the inside of the vessel. Unfortunately, sincethe vessels are not readily cleaned as they can be when inspectionpersonnel enter the vessel, there may be coatings of material over thesurfaces which prevent the detection of corrosion pits and the like inthe interior surface of the vessel unless the pits or otherirregularities have reached a size such that they can be detected by thelaser system.

Coke drums typically have an outer shell of carbon steel or alloy steel¾ to 1 ½ inches wall thickness and are internally clad with a layer offerromagnetic stainless steel (410 stainless steel, for example) whichcan be up to 2.5 mm thick. The drums contain girth welds with weld capsup to two inches wide. The caps are normally low profile.

Before any inspection, the coke is cut from the internal surface of thedrum using a high-pressure water cutter. This usually provides arelatively clean surface to enable the visual identification of crackindications.

Although very shallow craze cracking can exist in the liner, which doesnot in itself cause a problem, some cracks can grow to a significantdepth and even penetrate into the substrate shell. While visualindications of surface cracking can be identified using the visualsystem, it is not currently possible to classify the cracking for depthin order to assess the severity of the cracking. Currently insulationhas to be removed from the outside of the drum and ultrasonic testing isused to try and assess the crack depth. Apart from the cost involved inremoving and replacing insulation, the ultrasonic testing is hampered bythe cladding interface. Since these cracks can result in failures ifsevere, it would be highly desirable to determine the severity of thecracks, especially around weld areas, more easily and reliably and evenmore desirably in conjunction with the visual and laser testing.

SUMMARY OF THE INVENTION

A vessel inspection system for surveying the interior surface of adelayed petroleum coking vessel to identify defects in the vessel, thesystem including a device comprising: a frame; a support for supportingthe frame for movement within said vessel along an axis; a rotarypositioner adapted to position the frame rotationally with respect tothe axis, and a vertical positioner for raising and lowering the frame;a recording system adapted to record the rotary position of the framewith respect to the vessel and the position of the frame along the axiswithin the vessel; an enclosure for electronics and optionally a sourceof pressurized gas connected to the enclosure to pressurize theenclosure to minimize incursion of combustible vapor into the enclosure;a video camera supported on the frame and operably connected to at leastone of a monitor and a recording means for providing video monitoring ofthe interior surface of the vessel; a camera positioner supported on theframe and operable to position the video camera for viewing by the videocamera, the camera positioner being operable to position the videocamera about an axis perpendicular to the rotary positioner axis; afloodlight supported on the frame for illuminating the interior surfaceof the vessel for viewing by the video camera; a support on the vesselfor clamping the support in a predetermined lateral and verticalposition with respect to an axis of the vessel during operation of thesystem; an Alternating Current Field Measurement unit (ACFM), preferablymounted on a crawler positioned on an arm extension from at least one ofthe support and the frame for positioning the ACFM unit to test all orselected portions of the interior of the vessel; a crawler positionerfor positioning the crawler and ACFM unit in selected locations; and arecorder for recording signals indicative of the ACFM unit position andthe ACFM unit data from the selected locations.

A method for inspecting the interior surface of a delayed petroleumcoking vessel, the method comprising: positioning a camera and a cameralight in the vessel, the camera being positionable at a predeterminedcamera location relative to the longitudinal axis to record a video ofthe predetermined location; recording a plurality of videos at aplurality of predetermined camera locations and using the plurality ofvideos to provide a composite video of the interior surface of thevessel relative to the longitudinal axis; positioning an ACFM unit at apredetermined ACFM point on the interior surface of the vessel relativeto the longitudinal axis and determining the presence and severity ofcracks at the predetermined ACFM point; and determining the presence andseverity of cracks at a plurality of predetermined ACFM locations in aselected ACFM tested portion of the interior wall and using theplurality of determinations to produce a planar development of thelocation of cracks and the severity of cracks in the ACFM selectedportion of the interior wall.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevation of a prior art vessel inspection system shown inplace for inspecting the interior of a vessel, such as a delayedpetroleum coking drum;

FIG. 2 is a plan view showing a prior art stem clamp unit mounted on adrum top flange;

FIG. 3 is a front elevation of a prior art section device of the priorart system;

FIG. 4 is a side elevation of a prior art inspection device;

FIG. 5 is a schematic diagram of major elements of a prior art system;

FIG. 6 is a schematic diagram of an inspection device in a vesselshowing the positioning of a rotatable arm in its downward positioninside a vessel;

FIG. 7 is a view of a similar inspection device with the arm in anextended position;

FIG. 8 is a cross-sectional view of an inspection device in aninspection device in a vessel with the arm in an extended position;

FIG. 9 is a schematic diagram of the arm supported from a frame of aninspection device which also includes a camera and light source;

FIG. 10 is a schematic diagram of the system for detecting anddetermining the severity of cracks;

FIG. 11 is a schematic diagram of the system of FIG. 10 with the ACFMunit connected to the arm by a tether;

FIG. 12 exemplifies a crawler embodying features of the presentinvention for supporting the ACFM unit;

FIG. 13 is a perspective view exemplifying the crawler of FIG. 12positioned on an interior wall of a vessel to be inspected;

FIG. 14 is a top view of the crawler of FIG. 13;

FIG. 15 is a perspective view of the crawler taken within dashed outline15 of FIG. 13;

FIG. 16 is a view of the crawler of FIG. 12 taken within dashed outline16 of FIG. 14;

FIG. 17 is a view of the crawler of FIG. 12 taken along the line 17-17of FIG. 16;

FIG. 18 is a schematic diagram of the system, incorporating the crawlerof FIG. 12, for detecting and determining the severity of cracks; and

FIG. 19 is a schematic diagram of the system of FIG. 18 with the ACFMunit connected to the arm by a tether.

DESCRIPTION OF PREFERRED EMBODIMENTS

In the description of the Figures, the same numbers will be usedthroughout to refer to the same or similar components.

As noted previously, a system for photographing and inspecting theinside of a vessel for bulges and the like has been disclosed in U.S.Pat. No. 5,425,279 (the '279 Patent). The components of the presentinvention are suitably used in combination with the components of the'279 Patent, which are described as follows and in the '279 Patent.

Referring to FIG. 1, there is illustrated a major part of a vesselinspection system generally designated by the numeral 10. The inspectionsystem 10 includes a unique inspection device 11 shown disposed withinthe interior of a closable vessel 12 characterized as a delayedpetroleum coking drum, although the vessel inspection system is alsouseful with other types of vessels. The coking drum 12 is a generallycylindrical vessel having a cylindrical sidewall 14, a head 16 and afrustoconical lower distal end portion 18 terminating in a bottomdischarge opening 20 which may be closed by a suitable cover, not shown.The head 16 includes a cylindrical hatch delimited by a coaming 22, aflange 24 and a hinged cover 26 when in the open position. The vessel 12is typically covered with an insulating blanket 13 over substantiallyits entire exterior surface.

FIG. 1 illustrates the inspection device 11 connected to an elongatedstem 30 comprising a cylindrical pipe which extends into the interior ofthe vessel 12 through the manway or hatch coaming 22. The stem 30 ispreferably suspended from a suitable motor operated hoist 32 disposedabove the vessel 12 and operable to move the stem 30 from a raisedposition out of the interior 15 of the vessel to the position shown inFIG. 1 and to a further lowered position to allow the device 11 toinspect the entire interior surface of the vessel. In order tofacilitate the use of the system 10 to make high resolution videorecordings of the interior surface of the vessel 12 and to make precisemeasurements of distortion or dimensional changes in the general shapeof the vessel, it is important to stabilize and clamp the stem 30 duringoperation of the inspection system 10.

Referring to FIG. 2, the stem clamp unit 36 includes a generallyrectangular frame 38 having a chain type pipe clamp mounted on it, suchas a clamp type manufactured by The Rigid Tool Company. The chainencloses the stem to releasably grip the stem 30 to centralize it alongthe central longitudinal axis 48 of the vessel 12 and to prevent lateralor vertical movement of the stem during operation of the inspectiondevice 11. The stem 30 normally functions to carry a suitable cokedrilling apparatus at its lower distal end 31 such as a high-pressurewater jet type drill for cutting petroleum coke out of the interior 15of the vessel 12 for discharge through the bottom opening 20.

Accordingly, the inspection device 11 may be conveniently mounted on thedistal end 31 of the stem 30 in place of the drilling means, not shown.In this regard, a suitable coupling section 50 is provided for theinspection device 11 for releasably coupling the device to the lower endof the stem 30 when an inspection procedure is to be carried out.

Referring now to FIGS. 3 and 4, the inspection device 11 is furthercharacterized by an elongated frame 56, including an upper transverseflange part 58, which is suitably connected to a motor operated rotarypositioning mechanism 60. The rotary positioner 60 is also adapted to beconnected to the coupling part 50 and is operable upon command by remotecontrol, to rotate the inspection device 11, including the frame 56,with respect to the coupling 50 about a central axis 62 which, inoperation of the device 11, coincides with an axis 48 of vessel 10. Theframe 56 also supports an inspection or survey apparatus, generallydesignated by the numeral 66, for measuring the distance between an axis62 and an interior surface of the vessel.

The frame 56 includes a lower transverse flange 80 on which is mounted amotor operated positioning mechanism, generally designated by thenumeral 82, for supporting and positioning a camera 84 having a viewinglens 86 protected by an air curtain shroud 88. The camera 84 is suitablymounted on the positioning mechanism 82 for positioning the camera lens86. Accordingly, the camera 84 may be tilted about an axis 63 to viewthe entire interior surface of the vessel 12, for example. The camera 84is enclosed in an explosion-proof housing 85 and the air curtain shroud88 is also in communication with a conduit 74 to receive lens washinggas therefrom. The camera 84 may be of a type operable to have a minimumresolution of 300 equivalent standard television lines and may be of atype commercially available such as a Model SSC-C370 12vDc manufacturedby Sony Corporation of Park Ridge, N.J. The lens 86 may also be of atype commercially available such as a Model C-31002 manufactured byCosmicar and having a “zoom” or magnification ratio of about 12 to 1with remote control of zoom and focus.

As shown in FIGS. 3 and 4, the device 11 also includes a projectingfloodlight 90 which is operable to illuminate the interior surface ofthe vessel 12 for suitable viewing by the camera 84. The floodlight 90may be of a type available from Cooper Industries, Inc., Houston, Tex.,under the trademark Crouse Hinds as Model RCDE-6.

As shown in FIGS. 1 and 3, electrical control signals to and from thepositioner 60, the apparatus 66, the positioning unit 82, the camera 84and the floodlights 90 may be carried by suitable conductors, not shown,through a suitable junction enclosure 110 mounted on the frame 56 andthen through a suitable bundled conductor 112 which may be disposed in asleeve 114 together with the conduit 74. The multi-conductor cable andsleeve assembly 114 may extend from the interior 15 of the vessel 12,for example, through the bottom opening 20 to a suitable control consoleto be described in further detail herein.

As shown in FIG. 3, instrument air or purge gas may be conducted to asuitable control unit 116 mounted on the frame 56 and operable tomonitor the flow of purge gas to and from the enclosure 67 of theapparatus 66. The control unit 116 may also be of a type commerciallyavailable such as a Model 1101A, manufactured by BEBCO. Basically, thecontrol unit 116 monitors the pressure within the interior of theenclosure 67 and operates a suitable alarm if the pressure decreasesbelow a predetermined value indicating a possible leak of purge gas ofunacceptable proportion from the enclosure 67.

Referring now to FIG. 5, there is illustrated a block diagram of themajor components of the system 10 including those components disposed onthe frame 56. As illustrated in FIG. 5, the vertical positioning hoist32 is operable by a suitable controller 33 for positioning the stem 30and the device 11. FIG. 5 also shows the control console may be dividedinto two separate control panels, one for controlling the operation ofthe system 10 to make dimensional measurements or so-called bulgemeasurements of the section 14 of the vessel 12 and a separate controlpanel for operating the video camera 84. As illustrated in FIG. 5, acontrol panel 120 may be provided to include a controller 122 foroperating the rotation motor of positioner 60 and a digital computer orcentral processing unit 124 for controlling the operation of theinspection or survey apparatus 66 and for receiving data from theapparatus 66 to provide data and a suitable visual display of thedimensional changes in the surface of the section 14. The control panel120 also includes a rack mounted power supply unit 126 for supplyingpower to the apparatus 66. The power supply unit 126 is operable tosupply electrical power to the processing unit 124 also.

The processing unit 124 may be of a type operable to run on MS DOS basedsoftware, such as a so-called IBM type compatible computer. Theprocessing unit 124 is equipped with a suitable visual monitor 125 andkeyboard 127 and is adapted to be programmed to calculate, store andcoordinate data received from the apparatus 66 and display relatedimages on the monitor 125.

Referring further to FIG. 5, the control console also includes a videomonitoring control panel 130. A suitable audio and/or visual alarm 136is also provided on the panel 130 to indicate when a possible leak isoccurring in the enclosure 67 to the apparatus 66. As illustrated, thepanel 130 includes a suitable switch 138 for controlling the floodlights90, a control unit 140 for the tilt positioning unit 82 and a controller142 for operating the zoom lens 86.

The camera 84 is operably connected to a suitable power supply 144, avideo recorder 146 and a suitable video monitor 148, all at the panel130.

An operation to inspect the interior of a vessel such as the drum 12 ispreceded by removal of all material from the interior 15 of the vessel,opening the hatch cover 26 and providing access to the bottom opening20. The inspection device 11 can be inserted into the vessel througheither the top flange 24 or the bottom flange 20 depending uponrequirements unique to each site. In the embodiment shown, theinspection device is inserted through the top. Preferably, thetemperature within the interior 15 is reduced to about 100° F. and whenthe inspection device is inserted through the bottom, the stem 30 istypically lowered to a point so that the lower distal end 31 is belowthe bottom flange 20. The inspection device 11 is then connected to thestem which is then positioned vertically in the vessel such that thestarting elevation of the scan is coincident with the bottom tangentline of the vessel. The control cable assembly 114 leading to thecontrol console which includes the panels 120 and 130 is connected tothe device 11 and raised accordingly through the vessel 12. The seriesof operations is hereinafter referred to as “Bottom Entry Method”. Asimilar method is necessary to insert the inspection device 11 throughthe top flange 24, hereinafter referred to as “Top 5 Entry Method”. Atthis time the stem 30 may, if not previously adapted, be provided with asuitable linear measurement scale or tape measure, for example, suitablyconnected to its exterior surface for reference of the vertical positionof the device 11 once it is lowered into the interior 15. Alternatively,the hoist 32 may be provided with a suitable readout device to indicatelinear movement of the stem 30. Once the control cable 114 is suitablyconnected to the device 11 and to the control console, the inspectiondevice 11 is positioned at the starting point of the inspection and thechain clamp then secures the stem 30 prior to initiating the scanningsequence at a particular elevation. The position of the device 11 withrespect to the flange 24 is noted for each vertical change in positionof the device within the interior of the vessel 12.

When the device 11 has been positioned at the starting point of theinspection, the clamp unit 36 is installed on the flange with theclamping jaws 44 retracted so that they may be positioned around thestem 30. When the clamp unit 36 has been suitably secured to the vessel12 and the device 11 positioned in an initial position for inspectingthe interior of the vessel, the chain on the pipe clamp is secured tothe stem holding it in a centralized position aligned with axis 48.

Once the device 11 has been centralized and is ready for operation, aninert pressure gas or so-called instrument air is supplied through theconduit 74 to pressurize the enclosure 67 and to begin washing thelenses 68, 70 and 86. Proper pressurization of the enclosure 67 isverified through the control unit 116 by a lack of an alarm signal fromthe alarm 136. Verification of the operability of the positioners 60 and82 together with the operability of the camera 84 is verified.

At this point the floodlights 90 may be illuminated and an overall viewof the interior surface of the vessel may be initiated by operation ofthe camera 84 using the camera positioner 82 and the lens controller 142to cause the lens 86 to magnify an area of interest on the monitor 148.

According to the present invention, an Alternating Current FieldMeasurement (ACFM) unit is used to measure the severity of variousdefects in all or a portion of the inside surface of a vessel. Many suchvessels are used in industrial applications. Typically such vessels inthe past have been inspected by manual inspection by the use ofscaffolding and the like or by the use of techniques such as disclosedin the '279 Patent as disclosed above. Particularly, when a plurality ofinspections have been made over time, it is beneficial to compare theinspection results to each other. This enables the operator of thevessel to determine whether there have been changes in its dimensionsover time. The measurements by the laser unit are coordinated by the useof a positioning system which receives the data and coordinates it withthe position of the laser in the vessel. As indicated earlier, suchtechniques are disclosed in the '279 Patent.

This laser system is used in conjunction with a video camera and a lightsource so that the light source and video camera can prepare pictures ofthe inside of the vessel. These pictures are also coordinated so thatpictures are available for the entire internal surface of the vessel orany desired portion thereof. The coordination of the images is done bymethods well known to those skilled in the art.

By the use of this remotely positioned system, which includes the lasersystem, the video camera and light system mounted on a frame supportedinside the vessel, it is not necessary to clean the inside of the vesselprior to inspection, although the coke will have previously been removedusing a high pressure water jet. While certain features such as weldsand the like can be discerned, the inside of the vessel is not clean tothe extent that small corrosion pits and the like can be detected unlessthey reach a size such that they can be detected by the laser system orbecome visible. Even when visible, the use of the light and the laserdoes not provide information about the depth of any crack, especially ifthe crack is positioned at least partially under an interior cladding.

Accordingly, it would be highly desirable to determine the presence andseverity of these defects before serious corrosion or other types ofpitting can occur. Since these types of pitting are more common nearweld areas than over the entire vessel inside surface, in many instancesit may be desirable to inspect only the weld areas, although other areascan also be tested if desired.

Alternating Current Field Measurement (ACFM) is added to the currentinspection tool to provide crack detection and sizing capability. Themain use for the ACFM system is to distinguish between shallow surfacecracking (<2 mm (0.08″) deep) and more serious cracking which mayrequire further examination and evaluation.

ACFM is a proven tool for accurately sizing fatigue defects for lengthand depth in ferrous structures and is an electromagnetic technique fordetecting and sizing flaws breaking the inspection surface of bothferrous and non-ferrous metals and alloys. It operates using a probewhich induces a locally uniform alternating current (AC) field into thetest surface. This field flows in a thin skin in the surface of thematerial and is disturbed by the presence of surface breaking defects.These changes are detected by two types of sensors mounted in the probewhich measure the magnetic field strength in two orthogonal directions.One sensor, termed the Bx sensor, measures the reduction in flux densityaround the center of the crack which is predominantly caused by thedefect's depth. The other sensor, termed the Bz sensor, produces aresponse due to the curvature of the currents flowing around the ends ofthe defect. This sensor indicates the position of the defect ends andhence the surface length can be determined. The ACFM equipment iscomputer controlled and all inspection data is recorded for furtherinvestigation or for audit purposes. This system is capable ofinspecting through non-conductive coatings of up to 5 mm thick. There isa reduction in sensitivity to shallow defect as the coating thicknessincreases and it is usual to determine a compromise between maximumcoating thickness and minimum defect size.

According to the present invention an ACFM unit is used in combinationwith the camera and the laser to determine whether crack defects existin the vessel and determine the severity of such defects if present.While the ACFM unit could be used alone with a suitable positioning andrecording system, it is conveniently used in combination with the cameraand laser positioning systems to provide a complete vessel inspection.The camera enables the positioning of the ACFM unit at welds or otherareas which are visibly of interest for the ACFM testing. The ACFM unitcan be passed along welds and other areas which are more highlyvulnerable to stress cracking, corrosion, pitting and the like. Themeasured information is then passed to a recorder which coordinates itby reference to the position of the ACFM unit in the vessel. The ACFMunit positioned in the vessel could also be coordinated by use of thecamera positioning since it is desirable to use the light used incombination with the camera to light and photograph sections of theinside of the vessel during ACFM testing. The ACFM unit is desirablysituated on an extendable arm which permits it to be extended intocontact with the inside of the vessel.

In FIG. 6 a schematic diagram is shown of such a system. A vessel 12having a top 16 and a bottom 18 is shown. The system includes a camera(not shown) and floodlights 90 which are supported from frame 56. Anextendable arm 200, including on an end portion an ACFM unit 202, isshown in a downward position as mounted on frame 56 for entry intovessel 12. The frame is not shown in detail but can be similar to theframe disclosed above. The arm is mounted on the frame in a downwardlyextending direction. The arm is rotatable and includes an adjustablyextendable end portion to support the ACFM unit on a selected portion ofthe interior wall at a pressure sufficient to allow magnetic rollers(not shown) positioned on the ACFM unit to engage the wall and retainthe ACFM unit in close moveable contact with the wall. While magneticrollers are effective to engage the ACFM unit with the inside wall at adesired spacing and to move the ACFM unit along the surface, thesefunctions could also be performed by the arm.

The ACFM sensor head will be composed of an array of individual sensorsincorporated into an integral package. The size and spacing of thesensors are configured depending on the target defect size and otheroperating factors. A suitable sensor configuration will detect defectsof 0.25″ (0.4 mm) long×0.1″ (2.54 mm) deep. Different sensitivitiescould be used if desired. If it is desired that scan coverage is ofprime importance, individual sensor spacing would be set to theestimated maximum allowable for the detection of the minimum sizedefect. A typical sensitivity is listed below:

-   -   Number of channels: 32 (16 Bx and 16 Bz sensors)    -   Number of fields: 1    -   Sensor diameter: 5 mm (0.2″)    -   Sensor pitch: 7.2 mm (0.28″)

A suitable ACFM unit is available from TSC Inspection Systems as modelAmigo ACFM Vrack Microgauge. A variety of ACFM units may be useddependent upon the users and objectives.

Using twin fields provide information on transverse cracks and aids inthe identification and categorization of some spurious signals.Alternatively a single field could be used which would confine crackidentification and sizing to the circumferential direction, however itwould allow more sensors to be used for circumferential sensing leadingto a smaller spacing between sensors and/or a larger coverage. Suchvariations are well known to the art to achieve the specific objectivesof the user.

It is necessary to house some low power electronics in the sensorassembly itself to select and amplify the individual sensor readingsbefore transmission down the probe umbilical. The power supply to theACFM probe as shown is a 9 volt dual rail unregulated supply. Themaximum voltage that could be produced is 24 volts with a worst caseshort circuit condition leading to a maximum current draw of 1.5 A.

It is desirable to make the ACFM probe assembly as light as possible anddesirably the weight of the probe is less than one kilogram (2.2 lbs) ifconventional probe construction materials can be used for the outercasing. These materials are normally strong, machinable plastics.

Wheels or rollers may be fitted to the probe body to allow easy movementof the probe over the surface. These wheels may be magnetic and willdesirably hold the ACFM unit in close contact with the interior wall.Forced air cooling or other gases may be used for cooling or to limitthe pressure of combustible gases in the ACFM unit.

In FIG. 7 a similar vessel is shown with extendable arm 200 in a raisedposition and with the ACFM unit 202 extended into engagement with aninside surface 206 of vessel 12. A light zone 204 is shown on the insidewall of vessel 10 in conjunction with the location of ACFM unit 202.While desirably the light source is supplied by the same light sourcewhich supplies light for the camera and coordination of the camera andthe ACFM unit may be used to also identify the location of themeasurements taken by the ACFM unit, it is not necessary that this bedone. In other words, the ACFM unit could also be equipped with its' ownpositioning and monitoring system which could provide the data andlocation coordinates to a recording system.

In FIG. 8 the system is shown from a top view in more detail.Particularly, circles 208 and 210 are shown representing a typical cokedrum opening at the top with circle 208 representing the smallest cokedrum top opening known to Applicants. The inside of vessel 12 is shownas surface 206 with a frame 56 supporting extendable arm 200 to supportACFM unit 202 in contact with inside wall 206 of vessel 12. Extendablearm 200 includes an extensible portion 212 as shown. As known to thoseskilled in the art, data is readily collected and coordinated withrespect to the section of the inside surface of vessel 12 tested. Aspreviously indicated, it is anticipated that many users may selectivelytest only the inside of the welds on the inside of the vessel. The weldscan be readily located visually by the camera monitor.

In FIG. 9 a larger schematic diagram of an embodiment of the presentinvention is shown. In this embodiment ACFM unit 202 is shown in a lightcone 204 as it engages the inside 206 of the vessel. Extendable arm 200,including extensible portion 212, is positioned from a frame which alsoincludes a camera 84 and a light source 90.

While the ACFM unit has been shown as a wheeled unit which is maintainedin position by an extendable arm, it should be noted that the wheels maybe magnetized or non-magnetic. The requirement is for a suitably closeengagement with the inside wall of the vessel. The wheels may be drivenif desired or the rotational movement may be supplied by the extendablearm.

The system is shown schematically in FIG. 10. ACFM unit 202 ispositioned on inside wall 206 of vessel 12 by an extendable arm 212.Positioning data and test data re passed via a line 214 to acommunication device 216 and then via a line 218 to a PC controller 220powered via a line 222 by a 110 volt power supply. The ACFM unit issupported on a frame 56.

Such a frame also typically includes a laser system and a camera systemfor making the measurements described by the '279 Patent.

In FIG. 11 an embodiment similar to FIG. 10 is shown. In thisembodiment, however, the ACFM unit is supported on magnetic wheels at aselected distance from the inner surface of the vessel. The ACFM unitmoves by rotational power to the wheels at a selected pace. Therotatable arm trails the ACFM unit and supplies power, air and receivesdata and the like as necessary to achieve the desired testing via atether 224. The ACFM unit is free to move independently of theextendable arm to the extent it does not exceed the length of thetether. The ACFM unit is retrievable by the extendable arm by simplywithdrawing the tether and drawing the ACFM unit back into engagementwith the extendable arm.

A variety of mechanical arrangements can be used to achieve theseobjectives. Particularly the supply of air and power to the ACFM unitare supplied in substantially the same way as supplied to the laser andthe camera in the '279 Patent. Similarly, the data transmission from thelaser survey system, the camera system and the ACFM unit may betransmitted in the same way to a PC station or other computer station,where the data is analyzed and the profiles of the inside wall of thevessel and the like are prepared are accomplished in a similar fashionas known to the art.

Similarly ACFM units are well known as discussed in the various patentssubmitted in the Information Disclosure Statement submitted herewith.

By the method of the present invention, not only are bulges and otherlarge irregularities in the inner surface detected by the laser unit andnot only are surface observations possible but by the combination thelocation of the ACFM unit can be controlled using the same frame or asimilar frame as that used in the '279 Patent to analyze surface crackswhich previously could only be observed at the surface. This permits theowner and operator of a large vessel, which has been discussed herein asa coke drum but which could be any type of large vessel, to determinenot only whether the vessel has bulged or otherwise deformed but alsowhether there are dangerous cracks in the areas tested by the ACFM unit.This is a substantial advance in the testing of the vessel to ensuresafe operation and avoid catastrophic vessel ruptures and failures.

Upon completion of a survey of the vessel 12, the clamp assembly 36 isremoved from the flange 24 and the stem 30 is raised to remove thedevice 11 from the interior 15. The stem 30 is then returned to normaloperation and the inspection system 10 is removed from the vicinity ofthe vessel 12, including the aforementioned control console and relatedcomponents.

As discussed previously, the ACFM unit and the extendable arm aredesirably mounted on the lower portion of the frame at a distance belowthe lower portion of the frame sufficient to avoid interference with themotion of the camera in panning actions and the like. This permits theextensible arm to be extended downwardly carrying the ACFM unit into theinterior of the vessel. Upon reaching a selected level, the extensiblearm is rotatable to a substantially perpendicular position or to otherpositions as may be desired. The ACFM unit is then positioned againstthe wall of the vessel and moves either by its own motion(self-propelled) with magnetic wheels and a suitable driving motor or bymotion of the extensible arm around the vessel at a selected rate. Thesmaller the defects selected for detection, the slower the scanning ratemust be and the more sensitive the testing apparatus contained in theACFM unit must be. These criteria are readily selected by those skilledin the art for the type and size of defect which is to be determined.While it appears in FIGS. 10 and 11 that the cables are loose in vessel12, such is not the case. Typically the contact cables and the like arecontained in frame 56 so that the cables are relatively compact andcontrolled.

FIGS. 12-19 depict details of a vessel inspection system according to analternate embodiment of the present invention. Since the vesselinspection system contains many components that are identical to thoseof the previous embodiment, these components are referred to by the samereference numerals and will not be described in any further detail.

Accordingly, FIG. 12 exemplifies a crawler 1200 configured forsupporting the ACFM 202 according to principles of an alternativeembodiment of the present invention. The crawler 1200 preferablyincludes at least three wheels, preferably four wheels, 1202 which arepreferably magnetized to adhere to the inside surface 206 of vessel 12(FIG. 14) and allow viewing of surface welds close-up at various angles.Wheels 1202 are preferably provided with spring suspensions 1204 tofacilitate travel over rough-surface welds and weld overlays on theinterior surface. As discussed in further detail below, in addition toACFM unit 202, crawler 1200 also includes lights, lasers, and cameras.

FIG. 13 exemplifies the crawler of FIG. 12 positioned on an interiorwall of a vessel to be inspected, and FIG. 14 shows a top view of thecrawler of FIG. 13. FIG. 15 is a perspective view of the crawler takenwithin dashed outline 15 of FIG. 13.

FIG. 16 depicts the crawler of FIG. 12 taken within dashed outline 16 ofFIG. 15, and FIG. 17 is a view of the crawler of FIG. 12 taken along theline 17-17 of FIG. 16. As shown therein, the ACFM 202 is positioned onthe underside of the crawler, and is preferably centered thereunder. Acamera 1214 and light 1212 are also preferably positioned on theunderside of the crawler, proximate to ACFM 202 for viewing welds 226being tested by the ACFM.

A laser 1206 is positioned on a frontal portion of the crawler 1200 andis configured for projecting a line via a sheet of laser light 1207 foralignment with a weld 226 on the surface 206 of the vessel 12 to therebyfacilitate remote steering by an operator. The sheet of laser light 1207is oriented perpendicularly to the travel surface 206 of the vessel wallwhich then intersects the wall on a line, thereby casting a line,preferably on a weld bead, ahead of the centerline of the crawler. Acamera 1208 and light 1210 are also mounted on the frontal portion ofthe crawler 1200 and are oriented for viewing the sheet of laser light1207 preferably aligned with a weld 226. The cameras 1208 and 1214 arecoupled via line 214 to communication imagery data to device 216 andthen via line 218 to PC controller 220. It can be appreciated that thecombination of laser 1206, camera 1208, and light 1210 enable anoperator to guide the crawler 1200 precisely along a weld, resulting inmore reliable testing by the ACFM.

FIG. 18 is a schematic diagram of the system, incorporating the crawlerof FIG. 12, for detecting and determining the severity of cracks, andFIG. 19 is a schematic diagram of the system of FIG. 18 with the ACFMunit connected to the arm by a tether. In addition to positioning dataand test data, imagery captured by the cameras 1208 and 1214 is alsopassed via line 214 to communication device 216 and then via line 218 toPC controller 220.

Operation of the system depicted by FIGS. 12-19 is similar to operationof the system of FIGS. 1-11, but for additional data provided by thecombination of laser 1206, lights 1210 and 1212, and cameras 1208 and1214, which enable an operator to more precisely guide the crawler andtest the weld via ACFM 202, and visually observe close-up the inside ofthe inspected vessel.

By the use of the system of the present invention, not only can largebulges and the like be detected using the laser system and visibledefects detected by the use of the camera, but invisible defects whichmay be covered with residual material on the inside of a vessel can bedetected using the ACFM system. The ACFM units are well known to thoseskilled in the art for the determination of such defects in metalsurfaces.

According to the present invention, superior results are accomplishedsince visible defects, invisible small defects, such as corrosion pits,stress cracks and pits are readily detected as well as larger bulges andchanges in the inside dimensions of the vessel. This is a very desirableresult and is achieved by the use of a synergistic combination of thethree measuring techniques used. The present invention is particularlywell suited for use with delayed petroleum coking drums, sometimesreferred to as delayed petroleum coking vessels. These vessels haveopenings at both the top and the bottom, which are typically co-axiallypositioned relative to the vertical axis of the coking drum which issometimes referred to as a delayed petroleum coking vessel. The vesselsalso have a stem used to cut petroleum coke from the drum, but which canalso be used to position the frame. The coke is removed with ahigh-pressure water jet which may leave some areas, especially wherecracks or other defects may be positioned, less completely cleaned ofcoke. Testing of these defects is necessary to insure safe operation ofthe coking drum. Thus such vessels are well adapted to the use of thepresent invention and require testing which has not previously beenavailable without more expensive and time consuming processes.

While the invention has been discussed by reference to the drill stem ofa petroleum coking drum as a support for the frame, it should beunderstood that any suitable support capable of holding a frame at aselected axial location and a selected rotational and longitudinalposition relative to an axis may be used. Desirably the frame ismoveable longitudinally and rotationally relative to the inside of thevessel.

While the present invention has been described by reference to certainof its preferred embodiments, it is pointed out that the embodimentsdescribed are illustrative rather than limiting in nature and that manyvariations and modifications are possible within the scope of thepresent invention. Many such variations and modifications may beconsidered obvious and desirable by those skilled in the art based upona review of the foregoing description of preferred embodiments.

The invention claimed is:
 1. A vessel inspection system for inspectingthe interior surface of a delayed petroleum coking vessel to determinedefects and dimensional changes in the vessel, the system including adevice comprising: a frame; a support for supporting the frame formovement within the vessel along a vertical axis; a rotary positioneradapted to position the frame rotationally with respect to a verticalaxis; an enclosure for electronics and optionally a source ofpressurized gas connected to the enclosure to pressurize the enclosureto minimize incursion of combustible vapor into the enclosure; a videocamera supported on the frame and operably connected to at least one ofa monitor and a recording means for providing video scanning of theinterior surface of the vessel; a camera positioner supported on theframe and operable to position the video camera for viewing by the videocamera, the camera positioner being operable to position the videocamera about a second axis perpendicular to the rotary positioner; afloodlight supported on the frame for illuminating the interior surfaceof the vessel for viewing by the video camera; a support on the vesselfor clamping the support in a predetermined lateral and verticalposition with respect to the vertical axis of the vessel duringoperation of the system; a crawler positioned on an arm extension fromat least one of the support and the frame for positioning the crawlerproximate to all or selected portions of the interior of the vessel tobe tested; an Alternating Current Field Measurement (ACFM) unit mountedon the crawler for testing the all or selected portions of the interiorof the vessel; a laser mounted on the crawler for generating a sheet oflaser light along a weld for aligning the ACFM to the weld; a crawlerpositioner for positioning the crawler and ACFM unit in selectedlocations; and a recorder coupled to the ACFM unit for recording signalsindicative of the ACFM unit position and the ACFM unit data from theselected locations.
 2. The system of claim 1 wherein the crawlerincludes a camera and a light positioned on a frontal portion of thecrawler for viewing a weld line in front of the crawler.
 3. The systemof claim 1 wherein the crawler includes a camera and a light positionedon an underside of the crawler for viewing a weld line proximate to theACFM.
 4. The system of claim 1 wherein the crawler includes at leastthree wheels for facilitating movement along the interior of the vessel.5. The system of claim 1 wherein the crawler includes at least threemagnetic wheels for facilitating movement along the interior of thevessel with magnetic adherence to the interior of the vessel.
 6. Thesystem of claim 1 wherein the crawler includes at least three wheels forfacilitating movement along the interior of the vessel, at least one ofwhich wheels is mounted with spring suspension.
 7. The system of claim 1wherein the support is adapted to support the frame for movement alongthe vertical axis of the vessel and support the frame at a selectedvertical position relative to the vertical axis.
 8. The system of claim1 wherein a pressurized gas source is positioned in fluid communicationwith the frame to inject a gas stream into the frame at a pressuregreater than the pressure in the vessel.
 9. The system of claim 1wherein a pressurized gas source is positioned in fluid communicationwith the frame to inject a gas stream into the ACFM unit at a pressuregreater than the pressure in the vessel.
 10. The system of claim 1wherein the ACFM unit includes magnetic wheels to support the ACFM unitat a selected spacing from the interior surface of the vessel.
 11. Thesystem of claim 1 wherein the ACFM unit is self-propelled.
 12. Thesystem of claim 1 wherein the ACFM unit is moved relative to theinterior surface of the vessel by the arm extension.
 13. The system ofclaim 1 wherein the arm extension is extendible and retractable.
 14. Thesystem of claim 1 wherein the extendible arm is rotatable relative tothe vertical axis.